Recently, there has been an increasing thrust in the application of internal antennas in wireless communications devices. The concept of an internal antenna stems from the avoidance of using an external radiating element through the integration of the antenna into the communications device itself. Internal antennas have several advantageous features such as being less prone to external damage, reduced overall size of the communications device with optimization, and easy portability.
With the advent of mobile communications devices capable of operating in diversity function, designers have begun to use separate antennas in conjunction with a switching unit wherein each antenna operates in a distinct diversity performance. However, where multiple antennas are used in a device, their performance may deteriorate, in addition to necessitating usually unfavorable trade-offs between device size and performance. Such trade-offs can be that smaller devices may suffer performance problems, including shortened battery life and potentially more dropped calls, whereas devices with better performance require larger housings. In general, a key driver of this trade-off is mutual coupling between the antennas, which can result in wasted power when transmitting and a lower received power from incoming signals.